The invention relates to a helix-controlled fuel injection pump for internal combustion engines, in particular direct injection engine for commercial vehicles of tee type having a piston pump cylinder with control edges for controlling the supply of fuel to a pump working space via a fuel bore through the pump cylinder.
German patent specification No. 1,253,952 discloses a fuel injection pump in which, as well as a main injection piston, a further piston is used, which is intended for a pre-injection and the control collar of which controls the end of pre-injection. This fuel injection pump requires a not inconsiderable constructional effort and an overall height which is extended by the pre-injection piston and the spring arrangement.
An object of the invention is to simplify the fuel injection pump of the type mentioned above in terms of its technical construction and taking into account a compact overall height and of ensuring that the interruption in the injection produced by the control means is not impaired and thus contributes to noise reduction.
This object is achieved according to the invention by providing that the pump working space is bounded by a constant pressure relief valve and the pump piston, wherein the pump piston has an upper control edge and a lower helical control edge for controlling the fuel injection in dependance on the position of the pump piston and pump cylinder, wherein the pump cylinder is provided with a recess and the pump piston is provided with a peripheral groove for controlling pre-injection.
Providing the injection pump with a constant-pressure relief valve instead of an otherwise customary constant-volume relief valve has the advantage that the pressure lines leading to the injection nozzle are always completely filled with fuel. This consequently prevents the formation of voids or harmful spaces which do not allow for a complete interruption of the injection between the pre-injection and main injection phases.
The type of control means provided for effecting pre-injection, namely merely a recess in the pump cylinder and a peripheral groove on the pump piston with respective control edges, provides the possibility of controlling the pre-injection according to the requirements of the internal combustion engine, even load-dependently.
A further particular advantage achieved with the invention is that a functionally extremely effective pre-injection is achieved with the simplest of control means.
The measures as a whole greatly reduce troublesome harsh combustion noises.
The particular profile of the control edges relative to each other and the assignment of the peripheral groove on the one hand to the fuel bore hole and on the other hand to the recess allow for a rapid controlled opening and closing and thus an exact injection quantity characteristic effecting a strict separation between pre-injection and main injection according to certain especially preferred embodiments of the invention.
Further advantageous features of especially preferred embodiments make it possible, with a corresponding groove geometry, to effect the fuel interruption at any point. For example, to throttle the fuel interruption load-dependently, the cross-section of the peripheral groove is made smaller in the direction of partial load. Other measures serve to maintain substantially the pre-injection quantity, in spite of controlled pre-injection commencement, while other features influence the pre-injection quantity via the load.
In certain preferred embodiments an additional recess as peripheral groove in the cylinder for abrupt cutoff, for the purpose of introduction of pre-injection, reduces the dynamic component of the delivery rate in pre-injection, with the result that there is a reduction in the pre-injection quantity.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.